If you create a private or a public Party on Parsec, you can invite friends to join it via link sharing. There's a link to your party in the sidebar that you can share with them.
Even if someone hasn't received an invite to Party Finder, they can now join your party via a link! Your guest will only be able to join your party after you accept them. Unfortunately for them, they still won't have access to any other parties, but for now you can play games together.
They will then be directed to create their own account or sign into Parsec. Once they do that, they can request to join the party with a nice message.
Your guest will wait until you accept his request to join.
Once you accept the request to join, the guest can now request to Co-Play!